Effects of Alkali Metal (Li, Na, and K) Incorporation in NH2–MIL125(Ti) on the Performance of CO2 Adsorption

A series of titanium-based, metal–organic framework (MOF) materials, xM@NH2-MIL125(Ti) (x is the alkali metal loading percentage during the synthesis; M = Li, Na, K), have been synthesized solvothermally. Alkali metal doping in the NH2–MIL125(Ti) in situ solvothermal process demonstrated a vital modification of the material structure and surface morphology for the CO2 adsorption capacity at ambient conditions. By changing the reactants’ precursor, including different kinds of alkali metal, the morphology of xM@NH2–MIL125(Ti) can be adjusted from a tetragonal plate through a circular plate to a truncated octahedron. The variation of the alkali metal loading results in substantial differences in the CO2 adsorption. The properties of xM@NH2–MIL125(Ti) were evaluated via functional group coordination using FT-IR, phase identification based on X-ray diffraction (XRD), surface morphology through scanning electron microscopy (SEM), as well as N2 and CO2 adsorption by physical gas adsorption analysis. This work reveals a new pathway to the modification of MOF materials for high-efficiency CO2 adsorption.